Measurements of lens transparency or its disturbances by densitometric image analysis of Scheimpflug photographs.

Scheimpflug photography of the anterior eye segment with densitometric image analysis to measure lens transparency has proven its value in long-term follow-up studies of lens changes. The necessary technical conditions of the SL 45 Topcon camera guarantee high reproducibility. The technical control with respect to quality in case of repeated photography is ensured by an internal standard, the camera being equipped with a five-step scale of known density values. External standardization is done by taking the densitometer height of the cornea as standard. The coefficients of variation of internal and external standards were nearly equal (approximately 5%) over the 9-month period of observation of 100 patients (3,200 photos). The coefficients of variation correspond to the standard error found with repeated lens photos of volunteers' eyes evaluated by analysis of variance of the respective data sets. The standard error for distance measurements on the x-axis (cornea thickness, depth of anterior chamber, lens thickness, etc.) is less than 3%. Evaluation of follow-up examinations may most successfully be done by densitometric planimetry, which, in case of follow-up studies on opacified lenses, is superior to the usual measurements of densitometer height. The light scatter registered by Scheimpflug photography is highly individual. This is demonstrated by densitograms of normal lenses of persons of different age groups. Besides linear densitometry, various other procedures of densitometric planimetry are possible. The best results so far were obtained by multilinear densitometry, but the enormous amount of data obtained in this way renders routine application rather difficult.